Задание

Match the answers to the correct questions.

How are chemical changes different from physical changes?

Is toasting a piece of bread an example of a physical or a chemical change?

When bananas, berries, ice and milk are blended, does a physical or a chemical change occur? Why?

Is water evaporating an example of a physical or a chemical change?

What is a flame test and what can we learn from it?

What is a mixture?

Why is whipping egg whites a physical change?

Explain how the reaction of a flame to carbon dioxide is different from the reaction of a flame to hydrogen in terms of cause and effect.

What happens when you stir very hot water with a spoon made from gallium metal? What kind of change happens?

When you pour carbon dioxide gas onto candles, why do they go out one by one?

Chemical changes happen when substances change to form new ones, while physical changes do not form any new substances.

Heating bread in a toaster is a chemical change. The surface of the bread burns, forming a new substance.

Blending bananas, berries, ice and milk chops them up into tiny pieces, but doesn't create a new substance. Therefore, it is an example of a physical change.

Evaporation means to turn a liquid into a gas. Water in a gas form is not a new substance (it is still water), so that makes it a physical change.

A flame test is a way to tell different types of gases apart. Scientists know how different types of gas will react when exposed to a flame.

A mixture contains two or more substances that are not chemically combined. Mixtures can be physically separated into their individual components.

Whipping egg whites simply adds air into the egg whites, making them foamy. They are still egg whites (not a new substance), so this is a physical change.

Carbon dioxide displaces the oxygen the flame needs to burn, which causes the flame to go out (the effect). When a flame is placed near hydrogen, it causes a popping noise (the effect) as the hydrogen burns.

When you stir hot water with a gallium spoon, the metal melts. This is an example of a physical change because the gallium changed forms, but it didn't change into a new substance (it is still gallium).

Carbon dioxide gas is heavier than air. This is why it stays inside the pitcher. When you pour it at the top of the steps, it flows down the steps because it is heavier than the air that was there. When carbon dioxide displaces the air, a candle doesn't have enough oxygen, so it goes out. This process happens to each candle as carbon dioxide sinks lower and lower.